The present invention relates to a copier and, more particularly, to a copier in which a motor for driving a photoconductive element unit, a developing unit, a fixing unit and other various units and a motor for driving an optical system are installed independently of each other, the motor assigned to the units being comprised of a synchronous motor.
There has been proposed a copier in which a developing unit, a photoconductive element unit, a fixing unit and other units and an optical system are driven by individual DC motors, induction motors, synchronous motors or the like. However, a problem with DC motors is that they are expensive. Induction motors, on the other hand, are apt to slip and are variable in rotation speed depending upon the voltage applied thereto, resulting in a magnification other than a desired one in an intended direction of paper transport.
Synchronous motors are less expensive than DC motors and, at a predetermined frequency, rotatable at a fixed synchronous speed with no regard to the load. For this reason, a synchronous motor is extensively used with various units which are installed in a copier. Nevertheless, a synchronous motor is not fully acceptable when applied to a copier. Specifically, because loads are continuously exerted on a synchronous motor by, for example, the developing unit, photoconductive element unit and fixing unit as soon as the motor is energized, an arrangement has to be so made as to generate a starting moment which is as great as the rated load of the motor. This requirement cannot be met without making the motor and the copier bulky and without entailing temperature elevation inside of the copier.
Further, because a substantial load begins to act on the motor immediately after the start of the motor and because the input fluctuates, the motor becomes settled at a lower rotation speed than a predetermined synchronous speed before reaching the latter. The optical systm, on the other hand, is driven in synchronism with the synchronous speed of a synchronous motor and, therefore, the drive speed of the photoconductive element is lower than that of the optical system. In this condition, an image is somewhat reduced in an intended directin of rotation of the photocondutive element when formed on the element, appearing blurred or otherwise disturbed over the whole area.